1. Field of the Invention
The present invention relates to a seal structure as a constituent of the fuel cell and relates to a method for producing the seal structure.
2. Description of the Conventional Art
As a conventional seal structure for sealing gas or sealing a cooling passage in each cell of the fuel battery stacks, such a structure that a gasket made of an elastic member such as liquid rubber is formed on a separator is most commonly used (refer to Patent Documents 1, 2).
On the other hand, such a structure that a gasket is formed on a MEA (Membrane-Electrode Assembly) disposed between a pair of the separators has been proposed as follows:
(1) A seal structure wherein a resin film is applied or attached onto a peripheral portion of the MEA, and a gasket is formed on the resin film (refer to Patent Document 3), or
(2) A seal structure wherein gaskets are formed on both surfaces of a GDL (Gas Diffusion Layer) constituting an MEA by the injection molding of liquid rubber, and a part of the liquid rubber is impregnated within a porous structure of the GDL (refer to Patent Documents 4, 5).
Such conventional structures may fully achieve the desired objective to serve as sealing members. However, as for the former one (1), there is a problem that a number of component parts and a number of production processes are increased due to the necessity of employing the resin film, and as for the latter one (2), there is a problem that an undue pressure is applied to the GDL since compressive load of gasket is directly applied onto the GDL when a stack is assembled.
To eliminate the above-mentioned drawbacks, it is preferable to provide a structure that a rubber sheet is formed on a plane extending from an MEA at the outer peripheral side of the MEA, instead of surfaces of GDLs or the MEA, by injection molding of liquid rubber, a part of the liquid rubber is impregnated into a peripheral portion of a GDL to integrate the MEA and the rubber sheet, and lip lines having a gasket configuration are formed integrally on the respective surfaces of the rubber sheet. With such structure that the MEA, the rubber sheet and the lip lines are arranged along one plane, the resin film can be omitted and can prevent the compressive load of gasket from being directly applied onto the GDL.
With such flat arrangement, however, the liquid rubber is apt to be impregnated deeply in the plane directions of the GDL, since it is difficult to properly control the width (lateral length) of the impregnated area when a part of the liquid rubber is impregnated into the peripheral portion of the GDL in the manufacturing process thereof. As a result, there is a risk that the reaction area of the MEA, which is to be set widely at a central area of the GDL, becomes narrower to deteriorate the power generation of the fuel cell.    Patent Document 1: Japanese unexamined patent publication No. 2001-332275    Patent Document 2: Japanese unexamined patent publication No. 2004-63295    Patent Document 3: Japanese unexamined patent publication No.2003-7328    Patent Document 4: Japanese unexamined patent publication No. 2003-68332    Patent Document 5: PCT publication WO 2002/043172
The present invention is made by taking the above-mentioned drawbacks of the conventional art into consideration, and an object of the present invention is to provide a seal structure for a fuel cell with liquid rubber being impregnated into peripheral portions of GDLs constituting an MEA to form lip lines, wherein the width of rubber impregnated area can be properly controlled, and an MEA reaction area can be prevented from being narrowed to cause deterioration of power generation, and a method for producing the seal structure.
Further, in addition thereto, another object of the present invention is to provide a seal structure for a fuel cell, wherein the structure itself has capability for controlling the compressibility ratio of the lip lines, and thereby the lip lines can be closely contacted with separators in an appropriate posture, and a method for producing the seal structure.